Large corporations have for many years been concentrating their computer resources in data centers. This trend has accelerated over the last few years as server virtualization technology has become more and more prevalent. As data centers have become larger, some data center operators have begun to offer computing, storage, and network communication resources to outside customers who then become tenants of the data center. The offered services typically consist of elastic, on demand processing, storage that for most practical purposes is limited only by the tenant's ability to pay, and network bandwidth into the Internet. This development is called cloud computing.
Server virtualization technology allows a pool of servers to be managed as essentially one large computer resource. A layer of software called a hypervisor sits between the operating system and the hardware. The hypervisor schedules the execution of virtual machines (VMs) on a virtualized server. A VM is an operating system image packaged with some applications. The hypervisor allows a VM to be suspended and moved between servers to load balance. Load balancing and monitoring of VM execution to catch crashes provides the same kind of fault tolerance and scalability services for enterprise applications that are achieved at much higher cost with specialized solutions. These systems are referred to herein as a “cloud system.” A cloud manager system oversees the execution of VMs in the cloud system; scheduling execution to meet demand, to optimize server utilization, and to minimize power consumption. The cloud execution manager can schedule execution to allow in-service upgrade of hardware and software without impacting ongoing service provision.
In order to support arbitrary movement of VMs between machines, the networking within the cloud system must also be virtualized. Most cloud systems today virtualize the network by incorporating a virtual switch into the hypervisor. The virtual switch provides virtual network ports to the VMs executing under the control of the hypervisor. The virtual switch software also allows the network resources to be virtualized in a manner similar to how the server resources are virtualized by the hypervisor. The hypervisor and the virtual switch can thereby cooperate to allow VMs to be moved between servers. When the hypervisor moves a VM, it communicates with the virtual switch about the new location, and the virtual switch ensures that the network routing tables for the VM's addresses (e.g., a layer 2 Media Access Control (MAC) address, and the layer 3 internet protocol (IP) address) are updated so packets are routed to the new location.
Multicast is a system for the delivery of data to a group of subscribing nodes (e.g., VMs) by a source node. Some services provided by the VM within the cloud system could benefit from the implementation of a multicast protocol within the data center. However, such multicast protocol support is not supported by the cloud systems, because these multicast protocols require a large amount of control state to be maintained that exceed the capacity of the host machines and would diminish the performance of the data center and all cloud services.